| Summary: | Introduction: Myocardial wall stress (MWS) is thought to be the mechanical stimulus to ventricular hypertrophy (1,2). The objective of this study was to examine the effect of exercise on time-varying MWS (3).
Methods: Twelve subjects, aged 42.0 ± 16.8 (mean ± SD) years, systolic blood pressure (BP) (128 ± 11mmHg), were studied before and during peak bicycle exercise (85% of target heart rate). We estimated MWS from 3D transthoracic echocardiographic imaging of the left ventricle (LV) and LV pressure was derived from carotid tonometry during systole. Carotid pressure calibrated by mean and diastolic BP was used to calculate time-varying LV wall stress from endocardial and epicardial volumes obtained from Philips 3DQ analysis package. Time of onset relaxation (TOR) was defined as percentage of time to peak wall stress to ejection duration.
Results: There was a significant reduction in peak and mean MWS during exercise (rest 435.3±25.3 VS exercise 385.9±22.5, p=0.001 and 387.3±24.2 VS 368.7±19.6 kdynes/cm2, p=0.016), despite significant increase in systolic BP (128±3 VS 210±6 mmHg, p<0.001). LV end-diastolic volume (EDV) (119.3±9.4 VS 95.2±7.8ml, p<0.001) and volume at time of peak MWS (86.5±7.0 VS 68.3±6.3ml, p=0.001) were reduced significantly during exercise, but TOR was delayed (24.5±1.2 VS 31.0±1.6%, p=0.003).
Conclusion: Peak and mean MWS were reduced during peak exercise as a result of reduction in pre-load, despite of significant increase in systolic BP. But there was evidence of delayed myocardial relaxation during exercise.
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